The present application is directed to devices and methods for releasing tension on surgical tethers and, more particularly, to release mechanisms and methods that operate in vivo to release excessive tension on a tether.
The spine is divided into four regions comprising the cervical, thoracic, lumbar, and sacrococcygeal regions. Vertebral members of the spine are aligned in a curved configuration that includes a cervical curve, thoracic curve, and lumbosacral curve. Various deformities may affect the normal alignment and curvature of the vertebral members. Scoliosis is one example of a deformity of the spine in the coronal plane, in the form of an abnormal curvature. While a normal spine presents essentially a straight line in the coronal plane, a scoliotic spine can present various lateral curvatures in the coronal plane. The types of scoliotic deformities include thoracic, thoracolumbar, lumbar or can constitute a double curve in both the thoracic and lumbar regions. Schuermann's kyphosis is another example of a spinal deformity that affects the normal alignment of the vertebral members. One or more tethers may be attached to the vertebral members to reduce and/or eliminate the deformity.
Tethering is used with patients with growth potential of the bony members including prepubescent children less than ten years old who have yet to experience a growth spurt, and adolescents from 10-12 years old with continued growth potential. One issue with current tethering techniques is the inability to limit an amount of tension the tether applies to a vertebral member as the patient grows. This could lead to excessive stress on the bone interface. Current tethering techniques require a subsequent surgical procedure to lengthen the tether.
Tethering may also be used in other medical applications. One example is treatment of a fractured bone. In this context, the tether is attached to the bone on each side of the fracture. The tether is tensioned to apply a force that facilitates healing of the fracture. It may also be necessary to limit the amount of tension to ensure proper healing of the fracture.